The present invention relates to vane-type camshaft phasers for varying the phase relationship between crankshafts and camshafts in internal combustion engines; more particularly, to such phasers wherein a locking bolt is utilized to lock the phaser rotor with respect to the stator at certain times in the operating cycle; and most particularly, to an improved method for assembling such a camshaft phaser.
Camshaft phasers for varying the phase relationship between the crankshaft and a camshaft of an internal combustion engine are well known. In vane-type cam phasers, a variable locking bolt is typically included to permit rotational locking of the rotor to the stator under certain conditions of operation of the phaser and engine.
In a prior art assembly method, a locating pin is utilized to rotationally orient and fix the stator to a pulley or sprocket which drives the phaser in the engine. The pin not only sets the stator position during assembly but also holds the stator position during operation, as otherwise contact with the rotor can cause rotational movement of the stator with respect to the pulley, thus causing mis-timing of the engine. The rotational relationship of the stator to the pulley further controls the ability of the locking bolt mechanism, located in the rotor, to engage the pulley during service and to do so without excessive lock-bolt lash.
The prior art assembly method relies on several precision machined dimensions of the rotor, stator, pulley/sprocket, lock bolt, lock bolt bushing, and insert, which dimensions stack up to obtain a lock bolt engagement depth which allows the phaser to function through disengagement and re-engagement of the tapered lock bolt. These dimensions include the positions of the locator holes in the stator and pulley/sprocket for the locking pin(s). These precision dimensions can cause excessive cost in the manufacturing processes, in both in-house fabrication cost and direct material cost. Assembly of the phaser is also complicated such that dimensions in the lock bolt stack-up typically must be checked during every assembly to assure lock bolt function in the assembled phaser. Furthermore, the actual lock bolt engagement cannot be checked readily on a fully-assembled phaser and therefore must be checked during the assembly process, which causes variation in the assembly procedure and forces even tighter control of the process.
The problem exists in vane-type cam phasers employing either a straight-sided bolt or a tapered bolt. Since both axial and rotational lash can occur in the system, and since some lash is needed to assure that the bolt can both engage and disengage with the pulley/sprocket, what is needed is a simple method for setting the depth of engagement of the bolt and final rotational lash of the assembly prior to pinning the stator to the pulley/sprocket.
It is a principal object of the present invention to provide an improved method for assembling a vane-type cam phaser.
It is a further object of the invention to reduce the cost of manufacturing a vane-type cam phaser.
It is a still further object of the invention to improve the reliability of a vane-type cam phaser.
Briefly described, in an assembly process for a vane-type cam phaser, the pulley/sprocket is loaded onto a camshaft-shaped fixture with a camshaft nose. The camshaft nose feature is extended beyond the length of an actual camshaft nose such that a phaser rotor containing a locking bolt, when mounted onto the camshaft nose, is displaced axially by an amount sufficient to set the axial engagement of the bolt upon final assembly. The stator is loaded onto the pulley/sprocket and is rotated clockwise until it contacts the rotor, thereby removing all rotational and radial lash from the system. Then one or more axial holes are bored through the pulley/sprocket and stator and a locking pin such as a roll pin is inserted to permanently pin the stator to the pulley/sprocket. Finally, the partially-assembled phaser is removed from the cam-like fixture, the rotor is fully seated against the pulley/sprocket, the locking bolt is withdrawn from the pulley/sprocket, the rotor is rotated to an intermediate position, and the phaser cover is added to the assembly.